iommu/amd: Use try_cmpxchg64 in alloc_pte and free_clear_pte
Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in alloc_pte and free_clear_pte. cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, remove racy explicit assignment to pteval when cmpxchg fails, this is what try_cmpxchg does implicitly from *pte in an atomic way. Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20220525145416.10816-1-ubizjak@gmail.com Signed-off-by: Joerg Roedel <jroedel@suse.de>
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@ -258,7 +258,7 @@ static u64 *alloc_pte(struct protection_domain *domain,
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__npte = PM_LEVEL_PDE(level, iommu_virt_to_phys(page));
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/* pte could have been changed somewhere. */
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if (cmpxchg64(pte, __pte, __npte) != __pte)
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if (!try_cmpxchg64(pte, &__pte, __npte))
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free_page((unsigned long)page);
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else if (IOMMU_PTE_PRESENT(__pte))
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*updated = true;
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@ -341,10 +341,8 @@ static void free_clear_pte(u64 *pte, u64 pteval, struct list_head *freelist)
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u64 *pt;
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int mode;
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while (cmpxchg64(pte, pteval, 0) != pteval) {
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while (!try_cmpxchg64(pte, &pteval, 0))
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pr_warn("AMD-Vi: IOMMU pte changed since we read it\n");
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pteval = *pte;
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}
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if (!IOMMU_PTE_PRESENT(pteval))
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return;
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